Unloader for rotary compressors



Aug. 22, 1961 c. E. TERNENT UNLOADER FOR ROTARY COMPRESSORS Filed Dec. 1'7, 1958 IN VENTOR GEORGE E. TERNENT ATTORNEYS United States PatentO 2,997,227 UNLOADER FOR ROT Y 'COMPRESSORS George E. Ternent, Elyria, Ohio, assignor to Bendix Westinghouse Automotive Air Brake Company, Elyria, Ohio, a corporation of Delaware Filed Dec. 17, 1958, .Ser. No. 781,020 6 Claims. (Cl. 23031) This invention relates to fluid pressure systems and more particularly to fluid pressure systems utilizing a rotary compressor, a particular feature of the invention residing in the provision of improved unloader means for said compressor.

An object of the present invention is to provide in a fluid pressure system utilizing a rotary compressor of the sliding vane type, an improved unloading mechanism for the compressor.

It is another object of the present invention to provide an unloader for a rotary compressor which in unloading condition, permits a limited circulation of air from atmosphere through the compressor and back to atmosphere to prevent the creation of a high vacuum and consequent drawing-up of lubricant from the compressor lubricant supply reservoir.

It is yet another ,object of the invention to' provide an unloader which accomplishes the foregoing object and in addition provides means for limiting the partial vacuum to a substantially constant value regardless of the speed of the compressor so that the velocity of the small volume of circulating air will be su-fiiciently low to permit efficient separation at the compressor outlet of any lubricant picked up by the circulating air as it passes through the compressor.

Other objects and their attendant advantages will be come apparent when the following detailed description is read in conjunction with the single figure which illustrates schematically a fluid pressure system utilizing a rotary compressor and an unloader arranged and constructed in accordance with the present invention.

The system shown in the drawing comprises a conventional rotary compressor 10 preferably of the varied variety wherein sliding vanes are carried in a hub member and moved through a working cavity in a pump casing 11 by rotation of the hub which maybe integrally attached to a shaft 12 driven by an external power source such as the engine (not shown) of an automotive vehicle. The housing 11 is provided with an inlet port 14 which connects with the working cavity in casing 11 at its point of greatest volume and has an outlet .or delivery port 16 which connects with said cavity at a point of minimum volume so that as the vanes sweep air from the inlet portion of the cavity towards the outlet portion, the fluid is compressed in the decreased volume of the outlet portion and forced out through the delivery port 16'. The rotary compressor is not illustrated in detail because it is of well-known construction and operation and further description is not considered necessary.

Connected to the delivery port 16 is a fluid conduit 18 which leads into one end of an oil separator 20 whose purpose is to filter or separate from the compressed air flowing through line 18 oil entrained in the air as it flows through the compressor, the oil being present in the compressor for lubrication purposes. Separated oil flows to a suitable sump (not shown) through a conduit 22 and compressed filtered air flows from separator 20 through a conduit 24 containing a check valve 26 and thence into a fluid pressure reservoir 28 having the usual outlet connection 30 leading to an actuating device, for example, a brake valve. Leading also'from the reservoir 28* isa second conduit 32 connected to oneside'ofac'onventional fluid pressure governor 34 whose opposite side is connected by a conduit 36 toan unloader mechanism gen- Patented Aug. 22,1961

erally indicated by the numeral 38 and hereinafter described in detail. The governor 34 is of the type which is responsive to a predetermined high pressure in reservoir 28 for connecting conduit 32 with conduit 36 so as to admit reservoir pressure to the unloader to unload the compressor until such time as the reservoir pressure falls to a predetermined low pressure, at which time the governor operates to disconnect conduit 32 from conduit 36 and simultaneously to connect the latter to atmosphere thereby permitting the unloader to operate so as to load the compressor.

The unloader 38 comprises a body which is divided into an atmospheric cavity 40 and a bypass cavity 42 with the former being connected at all times with atmosphere through a port 44 and the latter being connected at all times with conduit 24 on the clean-air side of the separator 20 by way of a conduit and port 46, 47. Cavity 40 contains an internal bore or passage 48 forming a cavity which is connected at all times by Way of an outlet port and conduit 50, 52 with the aforementioned compressor inlet port 14. The passage 48 also communicates by Way of a port 54 with a valve chamber 55 having at one end a port 56 connected with atmosphere through port 44, with port 56 being controlled by a valve 57 which is retained normally closed by a spring 58.

The bypass chamber 42 communicates with inlet chamber 40 through a port 60 which is maintained normally closed by a valve 62 carried on one side of a valve body 64 which is normally urged to the left in the drawing to force valve 62 into sealing engagement with a valve seat surrounding port 60 by a spring 65 in the atmospheric cavity 40. On the side of valve body 64 opposite Valve 62 is a second valve member 66 which is adapted to sealingly engage the left-hand end 68 of passage 48" when the valve body 64 is moved to the right in a manner to be described;

At the left-hand end of the unloader body there is a control cavity 70 which is connected with the aforementioned governor conduit 36 through a port 72. Slidingly received in the chamber 70 is a piston 74 having a plunger 76 integrally connected thereto and extending axially through a sealed aperture in a wall 78 separating cavities 70, 42'. The end of plunger 76 is adapted to engage valve body '64 through port 60 to move body 64 from the position of the drawing to a position seating valve 66 against end 68 of passage 48 whenever control pressure from governor 34 is admitted to the left-hand side of piston 74.

The parts of the unloader 38 are shown in their compressor loading positions wherein the inlet 14 of the compressor is connected to atmosphere through conduit 52, passage 48, cavity 40 and port 44. Atmospheric air drawn in through compressor inlet 14 is compressed and forced through delivery port 16 and flows to reservoir 28 by way of conduit 18, separator 20, conduit 24, and check valve 26. Compressed air at the clean-air end of separator 20 also flows by way of conduit 46 to bypass cavity 42 in unloader 38 but the pressure admitted to chamber 42 has no function and is insufficient to unseat valve 62 against the force of spring 65.

When the pressure in reservoir 28 reaches a predetermined high pressure, this pressure acts through conduit 32 and operates governor 34 to connect conduit 32 with conduit 36 to admit reservoir pressure through port 72 to the left-hand side of piston 74 which moves rapidly to the right unseating valve 62 and seating valve 66 thereby connecting bypass conduit 46 with atmosphere through port 44 and disconnecting the compressor inlet port 14 from its free communication with atmosphere through passage 48 and port 44.

With the compressor inlet cut off from atmosphere, a vacuum is immediately created in conduit 52 arid passage 48. This vacuum increases until the force of atmospheric pressure acting on the left side of valve 57 exceeds a predetermined force of spring 58 at which point valve 57 cracks and admits atmospheric air to valve chamber 55 and thence through ports 54, 50 to the compressor inlet. This limited quantity of air passes through the compressor and flows substantially unimpeded through conduit .18, separator 20, conduit 46, bypass chamber 42 and thence to atmosphere through ports 60, 44.

The function of the limited quantity of air entering the compressor inlet through valve 58 is to insure that a substantially constant partial vacuum is created in the compressor. The partial vacuum is a function of the loading of spring 58 acting on the valve 57 and this loading can be selected to limit the vacuum created in the compressor to an amount which is insufiicient to draw up in a reverse direction lubricant from the compressor lubricant supply reservoir. However, since lubricant must at all times be supplied to the compressor, the vacuum-limiting air circulating through the compressor also serves to pick this lubricant up and pass it through the separator at a substantially constant relatively low velocity for eflicient separation and return of the lubricant to the lubricant reservoir in the normal manner. It will be understood by those skilled in the art that an automotive engine-driven compressor continually operates at varying speeds. In accordance with the invention, a substantially constant partial vacuum is permitted in the compressor regardless of the speed thereof by the spring-loaded valve 57 which would open a varying amount depending on the compressor speed to pass sufiicient air through the compressor in proportion to compressor speed to satisfy the desired partial vacuum requirements. Further, since the flow of lubricating oil tends to increase with compressor speed increase, the greater flow of air permitted by the unloader at greater speed will insure oil separation approximately proportional to the compressor speed. This same effect would not be possible if a bleed-hole were substituted for the valve 57 since, as those skilled in the art will readily understand, the capacity of a bleed-hole is limited and could not supply the required quantity of air to the compressor to provide the desired constant partial vacuum for all speeds of the compressor.

When the pressure in the reservoir 28 has fallen to a predetermined low value, the governor 34 is operated to disconnect conduit 32 from conduit 36 and to exhaust the latter to atmosphere. '65 immediately acts on valve body 64 to move it to the left, opening passage 48 to free communication with atmospheric port 44-. Immediately thereafter port 60 is closed by valve 62 to disconnect bypass conduit 46 from port 44 so that the compressor is then fullyloaded to supply fluid pressure to reservoir 28 through the separator 20 in the normal manner.

From the foregoing description it will be apparent that the present invention provides in combination with a fluid pressure system employing a continuously operating rotary compressor, an unloader for the compressor which cuts 01f the supply of fluid pressure to a reservoir when the pressure therein exceeds a predetermined high value, a particular featr re of the invention residing in valve means incorporated in the unloader for supplying a limited quantity of air to the compressor when in unloaded condition for providing a substantially constant partial vacuum in the compressor and for continually circulating or removing oil from the compressor while in its unloaded condition.

It will be apparent to those skilled in the art that the embodiment of the invention shown and described is exemplary only and that many modifications and changes may be resorted to without, however, departing from the scope and spirit of the appended claims.

What is claimed is:

1. In combination with a rotary compressor having inlet and delivery ports, means for unloading said com- Upon this occurrence, spring pressor comprising a valve body having a first atmospheric port and an outlet port connected to the inlet port of said compressor, valve means in said body movable to connect and disconnect said first atmospheric and outlet port, means movable in response to the delivery pressure of said compressor for moving said valve means, means for conducting said delivery pressure from said delivery port to said movable means, a second atmospheric port -connected to the inlet of said compressor and a spring loaded valve normally closing said second atmospheric port and being movable in response to the vacuum developed at said compressor inlet to admit a limited amount of air to said compressor inlet when said valve means is moved in said valve body to disconnect said first atmospheric and outlet port.

2. In combination with a rotary compressor having inlet and delivery ports, means for unloading said compressor comprising a valve body having a first atmospheric port, an outlet port connected to the inlet port of said compressor, and a bypass port connected to the delivery port of said compressor, valve means in said body movable to connect and disconnect alternately said bypass and outlet ports with said first atmospheric port, means movable in response to the delivery pressure of said compressor for moving said valve means, means for conducting said delivery pressure from said delivery port to said movable means, a second atmospheric port connected to the inlet of said compressor and a spring loaded valve normally closing said second atmospheric port and being movable in response to the vacuum developed at said compressor inlet to admit a limited amount of air to said compressor inlet when said valve means is operated to disconnect said first atmospheric and outlet ports and connect said bypass and first atmospheric ports, said limited amount of air admitted to said compressor by said spring loaded valve being bypassed to atmosphere through said last named ports.

3. In combination with a rotary compressor having inlet and delivery ports, a fluid pressure reservoir connected to said delivery port and a fluid pressure governor connected to said reservoir, unloader means for said compressor comprising a valve casing having a first atmospheric port, an outlet port connected to the inlet port of said compressor, a bypass port connected between said compressor delivery port and said reservoir, and a control port connected to said governor, valve means in said casing movable to connect and disconnect alternately said bypass and outlet ports with said first atmospheric port, pressure responsive means in said casing movable in response to the flow of fluid pressure between said control port and said governor and operatively connected to said valve means, a second atmospheric port in said valve body connected to said outlet port, a spring loaded valve normally closing said second atmospheric port and being movable in response to the vacuum developed at the inlet port of said compressor to admit a limited amount of air to said compressor inlet port and from thence through said delivery and bypass ports to atmosphere when said governor causes said pressure responsive means to operate said valve means to connect said, bypass port with said first atmospheric port and disconnect the latter from said outlet port.

4. In combination with a rotary compressor having inlet and delivery ports, a fluid pressure reservoir connected to said delivery port, a check valve connected between said delivery port and said reservoir, and a fluid pressure governor connected to said reservoir, unloader means for said compressor comprising a valve casing having a first atmospheric port and cavity, an outlet cavity and port connected to the inlet port of said compressor, a bypass cavity and port connected between the compressor delivery port and said check valve, and a control cavity and port connected to said governor, valve means in said atmospheric cavity movable between first and second positions, said first position connecting the outlet and atmospheric cavities and said second position connecting said bypass and atmospheric cavities, spring means normally urging said valve means to its first position, a pressure responsive element in said control cavity operatively connected to said valve means for moving it from its first to its second position in response to fluid pressure delivered by said governor to said control cavity, a second atmospheric port in said body connected to said outlet cavity, a spring loaded valve normally urged to a position closing said second atmospheric port, said spring loaded valve being capable of being moved to open position by vacuum created at said compressor inlet port upon movement of said valve means to its second position.

5. In the combination of claim 4 wherein the spring loading of said spring loaded valve is of such magnitude 6 to permit a substantially partial vacuum to exist in said compressor at all times While it is unloaded regardless of the variations in the compressor speed.

6. In the combination of claim 4 and including an oil separator connected to said delivery port down-stream from the connection of said delivery port with said bypass port of said valve casing.

References Cited in the file of this patent UNITED STATES PATENTS 2,535,760 Sherman et a1. Dec. 26, 1950 2,728,517 Shumaker Dec. 27, 1955 2,840,110 Parsons June 24, 1958 2,881,796 Garraway Apr. 14, 1959 2,894,677 Nash July 14, 1959 

